It is well known that band saw blades during the operation of a band saw make evasive movements when the sawing material, for example an entire log or a beam or a board is guided from the front against the toothed side of the band saw blade. These evasive movements may be laterally inclined with respect to the feed direction, or the band saw blade may twist about an axis parallel to its running direction. The evasive movement may also appear periodically, i.e. as oscillations with one or more frequencies.
For avoiding such evasive movements numerous band saw blade guides have been proposed. These guides, in most cases, are configured as mechanical guides.
U.S. Patent Application Publication US 2009/0126549 A1 discloses a band saw as well as a method for positioning a band saw blade in space. This prior art band saw utilizes a magnetic guide in which a magnetic force is exerted on the band saw blade transversely to the feed direction and to the running direction by means of magnetic guide elements. Within one magnetic guide element two separate magnets may also be provided which are positioned one beside another along the feed direction and exert a first force on a front area as well as a second force on a rear area of the band saw blade. When these forces are unequal, then they exert a torque on the band saw blade about an axis parallel to its running direction. Therefore, one may counteract torsions within the band saw blade.
Within the course of the present invention one has now found that with the use of the above-described approach one may make substantial contributions to the stability and to the precision of the predetermined sawing direction of the band saw blade, however, it has turned out that there exist, moreover, higher-order components of movement, the contribution of which to the instability of the band saw blade increasing with the running velocity of the band saw blade. These components of movement, for example consist of undulated movements in the running direction of the band saw blade.
German Utility Model publication DE 201 05 845 U1 describes a magnetic band saw positioning apparatus. This apparatus essentially consists of a U-shaped guide, the legs of which extending on both sides of the band saw blade to be positioned. The guide as a whole is supported against a stationary base via springs in the feed direction of the sawing material. A row of opposing magnets, obviously permanent magnets, is housed in the two legs of the guide, the rows extending parallel to the longitudinal direction of the band saw blade. In a first embodiment of the apparatus, the row is positioned beside the tooth base of teeth of the band saw blade. In a second embodiment of the apparatus the row is positioned behind the rear edges of elongate saw blade holes arranged along the longitudinal direction. Nothing is said within the publication as to the polarization of the magnets and their interaction with the band saw blade. The legs of the guide are dimensioned so long and the guide is positioned relatively to the band saw blade such that the rear side of the band saw blade keeps a distance from the flange interconnecting the legs. Thereby, the band saw blade may be somewhat shifted in the feed direction in spite of the magnets action when high feed forces occur, wherein, finally, also the elastic support acts as a limit. The guide exclusively affects a support of the band saw blade against the feed direction and, hence, counteracts only the little critical evasive movements. Lateral evasive movements or a torsion of the band saw blade are not avoided by this prior art guide which, hence, does not contribute to the quality of the sawing cuts with respect to dimensional precision or surface quality.